1. Field of the Invention
This invention generally relates to methods of chemical synthesis and, more particularly, to methods for synthesizing antimony selenide nanostructures in a variety of shapes.
2. Description of the Related Art
In the current development of modern photovoltaics there is a significant demand for new materials that can potentially act as a substitute for conventional silicon. Such research and development has given rise to the cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) solar cells, based on thin films technology. Moreover, hybrid organic/inorganic perovskite materials have recently emerged as sensitized architectures as a result of the constant search and evaluation of new materials as absorbers in solar cells.
Among the materials offering promise in the fabrication of solar cells, antimony—based chalcogenides represent a special subgroup. In comparison to many other materials, antimony—based chalcogenides are relatively non-toxic, earth abundant, and quite stable. The nature of their binary composition should suggest relatively simple antimony sulfide and antimony selenide preparation and handling methods. The physical properties of antimony chalcogenides, particularly the positions of the conduction and valence bands relative to the band structures of conventional electron and hole transporting materials, make them appealing candidates for photovoltaics. In addition, antimony sulfide has the advantage of an optical band gap of around 1.6 electronvolts (eV), making this material an almost ideal candidate for the tandem solar cells. In contrast, antimony selenide is a narrower band gap semiconductor material suitable as an absorber in single junction solar cells.
In particular, the most common application of antimony sulfide and antimony selenide relies on a sensitized architecture involving the mesoporous titania scaffold. Such a mesoscopic architecture provides some tolerance to the materials quality. Moreover, the band structure of both antimony semiconductors allows for the fabrication of solid sensitized solar cells. Such a device structure permits a device photovoltaic performance of up to 8.4%. However, as of yet, thin film antimony selenide solar cells have not demonstrated such efficiency. It is currently assumed that the poorer performance of antimony selenide is due to the defect states formed during the materials preparation or poor interface formation, even though selenide has been shown to produce significant photocurrents (ACS Appl. Mater. Interfaces, 2014, 6 (4), pp 2836-2841).
Due to the seemingly simple methods of preparation suggested by the binary nature of the material, the most common approaches for the formation of the antimony selenide have included the electrodeposition of both elements, or a chemical bath deposition. In both cases, the forming materials are initially amorphous and require an additional annealing step for conversion into a crystalline semiconductor phase. Those techniques generally provide materials with the diminished quality, resulting in the poor performances in solar cells, which mostly originates from the random distribution of the crystallites and defects within the absorber material of a solar cell.
It would be advantageous if antimony chalcogenide structures could be fabricated with a greater detail of control over their shapes and crystallinity.